Submersible electrical pump assemblies (“ESP”) are commonly used to pump well fluids from hydrocarbon wells. A typical ESP includes a pump, normally centrifugal, driven by an electrical motor. At least one seal section connects between the motor and the pump to seal motor lubricant in the motor. The seal section has a drive shaft with a thrust runner that engages a thrust bearing base to transfer down thrust imposed by the pump drive shaft on the seal section drive shaft. The seal section may also have a pressure equalizer to reduce a pressure differential between the motor lubricant and well fluid on the exterior.
Some installations employ seal sections in tandem, each having a thrust bearing. Because of tolerances, it is difficult to construct the seal sections so that a desired amount of sharing of the down thrust occurs between the thrust bearings of the two seal sections. One of the thrust bearings may wear too quickly relative to the other.